Positive active material, method of manufacturing the same and rechargeable lithium battery including the same

Abstract

One or more example embodiments of the present disclosure provide a positive active material, a rechargeable lithium battery including the same, and a method of preparing the same. The positive active material includes a lithium-containing composite oxide; and a sulfur-containing inorganic lithium compound, wherein the sulfur-containing inorganic lithium compound forms a coating layer on a surface of the lithium-containing composite oxide. The coating layer may reduce an amount of residual lithium and gas present on the surface of the lithium-containing composite oxide, thereby improving the stability of the battery and improving the cycle-life characteristics.

What is claimed is: 
     
         1 . A positive active material for a rechargeable lithium battery, comprising:
 a lithium-containing composite oxide; and   a sulfur-containing inorganic lithium compound,   wherein the sulfur-containing inorganic lithium compound forms a coating layer on a surface of the lithium-containing composite oxide.   
     
     
         2 . The positive active material of  claim 1 , wherein an X-ray photoelectron spectroscopy (XPS) binding energy peak of the sulfur-containing inorganic lithium compound is exhibited at about 168 eV to about 172 eV. 
     
     
         3 . The positive active material of  claim 1 , wherein the sulfur-containing inorganic lithium compound comprises lithium sulfate. 
     
     
         4 . The positive active material of  claim 1 , wherein the lithium of the sulfur-containing inorganic lithium compound is derived from the lithium-containing composite oxide. 
     
     
         5 . The positive active material of  claim 1 , wherein the coating layer has a thickness of about 1 nm to about 100 nm. 
     
     
         6 . The positive active material of  claim 1 , wherein the sulfur-containing inorganic lithium compound is included in an amount of about 1 wt % to about 20 wt % based on a total weight of the positive active material. 
     
     
         7 . The positive active material of  claim 1 , wherein the coating layer is formed as a uniform film on the surface of the lithium-containing composite oxide. 
     
     
         8 . The positive active material of  claim 1 , wherein a nickel content of the lithium-containing composite oxide is greater than or equal to about 55 at % based on a total amount of metals except lithium. 
     
     
         9 . The positive active material of  claim 1 , wherein a nickel content of the lithium-containing composite oxide is greater than or equal to about 80 at % based on a total amount of metals except lithium. 
     
     
         10 . The positive active material of  claim 1 , wherein the lithium-containing composite oxide comprises a lithium nickel composite oxide represented by Chemical Formula 1:
   Li a (Ni x M y ′M z ″)O 2 ,   <Chemical Formula 1>
   wherein, in Chemical Formula 1, M′ is at least one element selected from Co, Mn, Ni, Al, Mg, and Ti, M″ is at least one element selected from Ca, Mg, Al, Ti, Sr, Fe, Co, Mn, Ni, Cu, Zn, Y, Zr, Nb, and B, 0.8 <a≤1.2, 0.6≤x≤1, 0≤y ≤0.4, 0≤z≤0.4, and 0.6≤x+y+z≤1.2.   
     
     
         11 . The positive active material of  claim 1 , wherein the lithium-containing composite oxide comprises a lithium nickel composite oxide represented by Chemical Formula 2:
   Li a (Ni x Co y Mn z )O 2 ,   <Chemical Formula 2>
   wherein, in Chemical Formula 2, 0.8<a≤1.2, 0.6≤x≤1, 0≤y≤0.4, 0≤z≤0.4, and 0.6≤x+y+z≤1.2.   
     
     
         12 . The positive active material of  claim 1 , wherein the positive active material has a specific surface area (BET) of about 0.01 m 2 /g to about 10 m 2 /g. 
     
     
         13 . A method of preparing a positive active material for a rechargeable lithium battery, comprising:
 injecting a metal hydroxide precursor and a lithium source to form a mixture; and   firing the mixture at a reaction temperature of about 700° C. to about 800° C.,   wherein a sulfur-containing gas is injected during the firing while decreasing the reaction temperature.   
     
     
         14 . The method of  claim 13 , wherein an injection temperature of the sulfur-containing gas is about 400° C. to about 600° C. 
     
     
         15 . The method of  claim 13 , wherein an injection time of the sulfur-containing gas is from about 10 seconds to about 300 seconds. 
     
     
         16 . The method of  claim 13 , wherein an injection amount of sulfur-containing gas is about 0.1 L/min to about 2 L/min. 
     
     
         17 . The method of  claim 13 , wherein the sulfur-containing gas comprises about 5 volume % to about 100 volume % of a sulfur dioxide (SO 2 ) gas. 
     
     
         18 . The method of  claim 13 , wherein the lithium source is further injected during injecting the sulfur-containing gas. 
     
     
         19 . A rechargeable lithium battery, comprising:
 a positive electrode comprising the positive active material of  claim 1 ;   a negative electrode;   a separator between the positive electrode and the negative electrode; and   an electrolyte solution between the positive electrode and the negative electrode.